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Is it possible (not practical) to create a liquid nitrogen jet?
Would it be possible (though not practical) to create a jet that runs on liquid nitrogen that is heated, creating the expansion effect? I believe nitrogen takes up 674 (about) times as much space in gaseous form as in liquid, but if it were somehow evenly heated, could it provide a similar effect to combustion without the carbon emissions?

Thinking of a turbofan and nitrogen replacing the fuel in the combustion chamber...

But why take the trouble using nitrogen, why not water? That expands as dramatically as nitrogen does when heated to the boil.

Wouldn't you theoretically need a lot less energy to heat the nitrogen since it boils immediately in our atmosphere, where you'd have to have something really hot and thus more energy to boil the water? Overall energy is the same since you'd have to cool the nitrogen initially, but while in the air it's more efficient..

How would you cool the nitrogen? It has a boiling point of - 195 C.

That's named cold gas thruster. About efficiency you need to compare the specific impulse (76s) of N2 and the specific impulse of a turbofan (3000s). The lower the sp, the lower the efficiency.

How would you heat the nitrogen?  If with some sort of fuel, why bother?  It's more efficient to use the fuel directly in a conventional jet engine.  Only thing I can think of that might work is using it as reaction mass in some sort of NERVA-style nuclear engine: http://www.daviddarling.info/encyclopedia/N/NERVA.html

@ mins Yes specific impulse! Thank you, another drawer opened with some decades old, dusty morsels of knowledge in it.

@ oeste yes the nitrogen would boild, but it needs to boil before you propel it into the atmosphere.

@oeste: Boiling the nitrogen takes energy, which is extracted from the surroundings, thus cooling them.  In short order you reach a steady start where the rate of boiling is controlled by the heat flow rate - which is why you can store liquid nitrogen for quite a long time in well-insulated containers.  The gradual boiling off of a small amount cools the rest.

@Koyovis water based engine may work on Venus, where the air temperature is above the water boiling point.

It would work on earth as well. Steam engines have been around for a while.

You run into several major problems that make your entire assertion fundamentally flawed:

The liquid nitrogen needs to be constantly cooled and kept in heavy containers to remain liquid, greatly increasing the mass of your fuel tanks AND requiring some form of active cooling system that needs a source of energy to run on.
You then need to heat up the nitrogen as it enters the engine proper (through thick and heated pipes to prevent the pipes from getting quickly coated with a layer of heavy water ice, requiring more heating systems that require more energy), this requires a source of energy and thus more mass and fuel.

In the end you're going to need a large generator running some kind of fuel to produce the electricity needed to cool the liquid nitrogen, heat it up in the engine, and prevent icing on the nitrogen pipes. This would likely have the same mass, size, and fuel requirements roughly as the jet engine you're thinking to replace with a nitrogen expansion vessel.
And on top of that your fuel system for the main engines just got a lot more complicated, prone to failure (cryogenic systems are very prone to failure as all but the most exotic materials tend to not last very long at cryogenic temperatures, certainly when compared to normal temperatures), and heavier.
All these problems were encountered during the 1990s and early 2000s when several manufacturers (including Airbus and I think Boeing) started drawing up plans for aircraft fueled by liquid hydrogen.
Turned out that just the tanks and cooling/heating systems would take up the entire cabin space of say a 747 while giving the range and performance of something smaller than a 737 (while leaving it with no room for passengers or cargo).

Why cannot evaporation process cool the nitrogen? Some part of the fuel evaporates and goes into the engine, that remains stays liquid.

@h22 not enough, not by far. It helps, sure, but the incoming heat from the surrounding environment is far more than that unless you have incredibly large isolation vessels. A vessel that can keep a liter or so of liquid nitrogen in liquid state for a few hours weighs 5-10 kilos empty and has a volume of 5 liters or more. Now think what it'd take to keep several hundred tons of the stuff in liquid form...

The logic seems to be somewhat self-contradicting. If you don't isolate the tanks, you get a fairly high flow of nitrogen gas (from evaporation). That's the source of your trust (possibly with some further heating). You can heat the nitrogen steam directly as it exits the tank, preventing the pipes freezing. I think the main problem is that the tank ends up covered in ice, not the pipes. This is a real issue for rockets.

At best, the mechanical energy you can release by evaporating liquid nitrogen would be about its heat of vaporization, which is 5.56 kJ/mol or roughly 200 kJ/kg. (Converting this energy to useful thrust probably requires you to use the expanding nitrogen to drive a turbine that drives a fan or propeller, but that's a Simple Matter of Engineering, at least comparatively).
The chemical energy density of jet fuel is about 46 MJ/kg.
Even if we suppose the efficiency of your nitrogen engine could be a bit better than that of hydrocarbon-burning engines, this still mean that you would need to carry about a hundred times more nitrogen (by weight) than jet fuel for the same result.

Some of the nitrogen needs to be boiled off for auto-refrigeration as well, so a part of the 200 kJ/kg is used for keeping the fuel cool.

You could if you would cool the N$_2$ on the ground and then let it expand, you would then not need the compressor amd the turbine in your turbofan drawing, just an exhaust nozzle.
In a way you would use the liquid nitrogen as an energy storage source, like a battery. Possible, yes, practical, no, like stated in the question. A practical problem being the fuel tank that needs to be kept below -159 deg C for the nitrogen to remain fluid.
Another practical problem is that it would be a rocket engine, not a combustion engine. Rocket engines bring all their propellants on board, while a jet is an air breathing engine: most of what streams out of the jet exhaust is air, which was floating around in the atmosphere just where the plane was, now bound to carbon atoms from the fuel. That's what you need all the compressor and turbine blades for, to first compress outside air and then extract energy to run the compressor.
Rocket engines have an issue with how long the fuel lasts. All of the mass you're propelling to create thrust with, you carried on board and took off with. It could be an amusing exercise to compute how many passengers would be able to sit around the huge nitrogen tank with very cold feet from the -159 C fluid inside, ready for a flight of 3 minutes.
There was a clever Frenchman who sold licenses for compressed air vehicle motors some time ago, a wonderful scheme to extract money from people with more money than sense. It hasn't worked in a car yet due to it all being a bit inefficient - can't see it work in an aeroplane where weight is so important. But perhaps I'm just overly pessimistic, these could one day be just practical design problems that were overcome.
Edit
The question turned into a discussion that is more interesting than what I initially expected. A string of half-truths may look like a proper necklace at first glance.

Why would you use blades? It's a pure reaction thruster. Else efficiency is even lower.

If that's the case why is a standard combustion turbofan any different?

Yes why would there be blades.

@oeste Standard combustion releases internal chemical  energy, and ties air mass to the propelling gases.

wouldn't it be nice if you could create thrust out of thin air without putting in any energy (which you are describing here...)? Sadly the laws of physics don't allow for it.

@jwenting if the liquid nitrogen can be heated "for free", it can evaporate, expand and do the useful work. And it can be heated "for free" because the surrounding air has much higher temperature.

@h22 perpetuum mobile doesn't work...

@jwenting: Creating that tank of liquid nitrogen takes that energy. The challenge is, can we convert that energy back into mechanical energy with sufficient efficiency, using a light-weight and compact system ? As it turns out, jet engines are pretty good at that. The real problem is what Henning Makholm noted: it doesn't actually take that much energy to create liquid nitrogen. Or, alternatively, you need quite a bit of liquid nitrogen to store a given amount of energy.

Liquid nitrogen could be heated by the coming air (-50 celsius at flight altitude is not the best temperature but still way above the temperature of liquid nitrogen) and then expand. The engine would need lots of air to heat the nitrogen, so may actually need the air intake, compressor (compressing air raises the temperature a lot). Higher flight speed may be optimal, as such an engine would likely want higher intake temperature.
There is no need for such an engine to be pure rocket, it can have also bypass, using fan to accelerate some air bypassing the core, same as most of jet engines do.
Storing liquid nitrogen is also not a problem, as the process of evaporation (that must be even accelerated by the engine) should cool it enough.
Some thrust seems possible. Mathematical analysis by specialist in physics is required to figure out if the thrust would be sufficient to sustain the flight.

I can see the half truths being injected here. Yes compressing incoming air does heat it up, but where does the energy to do this come from. Thrust generation: whether pure expansion nozzle or with external fan does not really matter, just a few percentage points. But even if the fan is used, your still not tying oxygen atoms to the nitrogen and including that into the specific thrust.. Boiling off nitrogen to cool it makes it even less efficient. At what point does "impractical" turn into "forget about it"?

The energy comes from the temperature difference. Same way, if you have the electricity generating thermo-pair (one end in the liquid nitrogen, another in the air outside the aircraft), it would generate the electricity because there is a temperature difference for it to work. The fan may be required to extract enough heat from the rather cold surrounding air. At which point I need to say think again?

Yes a Stirling engine works. Yes a cold thruster creates thrust. And all of the other smoke pots that together create the smoke screen. But now look at the total energy contents of liquid nitrogen compared to that of kerosine and you'll find your "can't be done". If an expanding has engine was so great, why did the Space Shuttle not simply expand its LOX?

@Koyovis: The idea of a jet engine is to have a compressor in front and a turbine in the rear. That's where the energy comes from. This produces a net propulsion as long as the turbine extracts only a fraction of the power of the exhaust stream. In this scheme it would work as the compressed air flow is increased by the added nitrogen stream. However, this idea probably fails when it suggests a bypass. The turbine probably won't provide enough power for that.


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Do any newer production aircraft use venturis as a backup vacuum source?
I began my flight training in a Cessna 120 with 2 venturis as the source of vacuum for my DG and TC. They worked well in flight.
Are there any aircraft with deployed/deployable venturis out there? Other than my 1946 vintage C-120 which is also my birth year.

Not as far as I know. Even Vacuum pump systems are quickly becoming a thing of the past. Electric AI's are available and I have seen plenty in use. However with glass cockpits making their way into general aviation AHARS units are becoming more and more common place over traditional vacuum systems. There are even some small drop in units intended to replace traditional vacuum systems like DG's and Attitude Indicators. Venturi vacuums, while simple have down sides like potential icing risks and needing sufficient airflow to function.

A complete electrical failure in a non battery powered backup AI would still require a vacuum source.  Although I must admit the venturi became less visible on aircraft as I advanced through many different models through the years, until the complete absence in 'modern' IFR capable aircraft.

@mikebrass that is incorrect, to be certified as a backup electric AI the unit must have a second independent power supply not driven by the main system typically this is an internal backup battery but can be fed off a second electrical system in a twin engine scenario.

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sort: votes


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Do the spinning parts of the tail mounted jet engines produce yaw on pitch changes?
For example: on takeoff at rotation, would the clockwise rotation of the 2 engines have enough force to move the nose of the aircraft left? Precession would be the force, is it strong enough?

One comment in that Q/A was semi pertinent to my question. It may be an answer, but I do not know.

Location of the engine (wing or tail) shouldn't make a difference in the yaw effect. The F4U Corsair, for example, needed rudder trim for takeoff with a propeller engine mounted in its nose. Everything said about jets in the linked question should apply to your tail-mounted engine as well.

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Does TCAS II equipment satisfy the required ADS-B installation?
The title says it all.
If TCAS II is installed and functioning, does it satisfy the ADS-B OUT mandates?

They're not entirely separate. Some implementations of ADS-B use a 1090 MHz Mode S transponder, which is also a required component of a compliant TCAS II installation.  The position source required for ADS-B is separate, however. I think it's a reasonable question.

No to ADS-B OUT. Mode S transponders broadcast on 1090 MHz and can be designed to support ADS-B OUT. TCAS II receives on 1090 MHz so in addition to the TCAS function TCAS is capable of supporting ADS-B IN. Most of these ADS-B IN capable TCAS just receive the ADS-B messages, package them into reports and forward them to a separate processor that contains the ADS-B IN applications.

TCAS II and ADS-B are two entirely different systems, with entirely different functions, and they have different regulations. Having TCAS II installed & functioning does not satisfy any of the ADS-B OUT mandates.
ADS-B regulations European Union
For Europe, the regulations for ADS-B are published in the surveillance performance and interoperability requirements Implementing Rule (SPI-IR), Commission Implementing Regulation (EU) No 1207/2011, amended by Commission Implementing Regulation (EU)  No 1028/2014 and Commission Implementing Regulation (EU) 2017/386.
TCAS regulations European Union
TCAS II, version 7.1 is regulated by Commission Regulation (EU) No 1332/2011 amended  Commission Regulation (EU) 2016/918.


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Is a Phenom 300 single pilot able to fly non-commercially in Europe?
Can a personally owned Phenom 300 be flown non-commercially by a SP typed pilot in Europe?

What would make you question that it could?

Would the "authorities" in Europe deny my flight as the only pilot onboard?

I know you're asking about regulations, but insurance companies are often much stricter and that's always worth checking out too. Even if you're type certified and meet all the legal requirements, your insurer might want a minimum number of hours in type before covering you as a single pilot.


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If my parachute fails to open, why should I aim for land rather than water?
I was watching these 'what if' parachute failure videos on YouTube and everywhere they say do not choose water over land. Why should we not choose water and what happens if we land in water?
One such video:

You can't drown on land.

@GdD The meta consensus so far is that questions about parachuting (and paragliding) are on topic. Many modern parachutes are basically flying wings so it's hard to see why we'd exclude them (and that's not even considering the many ways that parachuting is relevant to aircraft pilots).

Aim for a hospital.

It will be easier to find your body.

If your parachute fails to open entirely you are almost certainly extremely dead no matter where you land, however occasionally people do survive. A partial failure of a chute is much more survivable. You will be coming down much faster than you would with a good chute, and you are going to get injured, probably badly. Think broken legs and arms with neck or back trauma. You may sustain a concussion as well, and you will certainly go into shock.
If you come down in the water you will be injured and unable to keep yourself afloat, and it will be much harder to rescue you. On land help will be much closer and, and as @RonBeyer says in comments, you can't drown on land.
Land has features which may help you survive: trees, vegetation, hay bales, crops, snow, and many other things may cushion your impact enough to make the difference between life and death. Water is the same wherever you go, and doesn't have nearly enough give to cushion an impact.

Some statistics: 100% (albeit being a small sample) of the persons listed here landed on land https://en.wikipedia.org/wiki/Category:Fall_survivors

@ViktorMellgren that's because it's possible to land on something yielding or on a steep smooth slope that can decelerate you at a survivable rate.  At freefall speeds water might as well be concrete for all the yield it can give.

might be good to add how hitting water at speed compares to hitting something solid

@Michael That depends very much on the attitude at which you enter the water.

related : Why is jumping into water from high altitude fatal?

Fantastic QA!  I was just wondering - there was always a myth that the one-and-only Evil Knievil wanted to jump with no parachute, and then steer himself (apparently) to fly fairly horizontally, then perhaps point "up" a bit, scrubbing speed, and top it all off by landing in a (say) big hay stack. Is this completely nonsensical?  Or in fact - would a sky diver in the worst case of a total failure, indeed try to "swoop" (at precisely the right time!) so as to trade away some vertical speed? Or again, is it utter hooey??  Cheers!

I think it's good to consider the maximum time you have if you land on water.  You probably won't be swimming after landing so you got about 3 minutes before you go unconscious.  You may end up sinking, and after 6-7 minutes you're gonna have permanent brain damage.  It's just a bad deal to go for water if you need a parachute.

@Fattie sounds like hooey.  My only reference though is that people using wingsuits also have normal chutes to deploy for landing.  They can't go slow enough or horizontal enough to land without.

Knievil came up with all sorts of schemes, some he was serious about and some he wasn't @Fattie. I suspect this is one he came up with to keep people thinking how crazy he was, he was a calculated risk taker and I don't imagine he liked how that one stacked up.

@ViktorMellgren my favorite part is how they separated the names out by letters, just to keep it more clear

Another factor--water is featureless.  Land sometimes has features that will ease your landing.  Look at Nicholas Alkemade--by pure luck he hit a pine tree & snow, leaving his injuries limited to a sprain (and even that's not certain as it could have happened before he jumped.)  He literally walked away from a 3 mile fall.

@Fattie - a no parachute wingsuit landing has been done, landing on "a stack of 18,600 cardboard boxes, 350ft long, 50ft wide and 12ft deep" - http://www.independent.co.uk/life-style/gadgets-and-tech/news/a-2400ft-jump-on-to-a-pile-of-boxes-with-no-parachute-what-could-go-wrong-for-stuntman-gary-connery-7778794.html https://www.youtube.com/watch?v=dRB-woVjlFY

And on water: https://www.youtube.com/watch?v=o2xmAWS4akE

utterly amazing:  youtube.com/watch?v=dRB-woVjlFY

Whether Evel Knievel could have come up with something close enough to a modern wingsuit to allow that in the 1970s, who knows. Maybe not, which is why he never tried it....

At terminal velocity, water is almost as hard as concrete due to the fact that it doesn't compress, (well technically does but only negligibly.) You wouldn't want to land on concrete, would you? Secondly, as mentioned earlier, you could very easily drown.

@armb - wingsuits go all the way back to the 1930's. Dying due to parachute failure at the end of a wingsuit flight dates to approximately the same time period.

@samdoj - if nothing else, hitting land may kill you quicker than hitting water. Some things you really don't want to drag out...

You could potentially keep yourself afloat, but you'd have to ditch your gear first.  And quickly.  That's a much bigger ask than merely floating in place until help comes.

@BobJarvis Wingsuits date back to 1912. But I still think Evel successfully using one without a parachute in the 1970s would require something closer to the modern one used in 2012 to do actually that.
"In the mid-1990s, the modern wingsuit was developed": https://en.wikipedia.org/wiki/Wingsuit_flying#History

@BrianLeishman It is funny, but it's not anything anybody did on purpose. It's just what MediaWiki servers do with category pages.

Extremely dead?  So is that different from just regular dead?

As anyone who has watched The Princess Bride would know, there are different levels of dead @CarloFelicione!

From a jump instructor, whose chute failed:

You landed in a blackberry bush, right? Yeah, it was less than a meter
high and it wasn't super dense but it was better than hitting than the
hard floor or hitting the lake. If I'd landed in the water I would
have been knocked out just the same and broken the exact same bones.
But my lungs would have collapsed and I would have drowned, because I
was unconscious.

So this instructor had studied the problem enough to know that he didn't want to land in the water.  He is not alone.

How to fall 15,000 feet, hit the ground, and survive (2016)

Also, years ago, I remember meeting a woman who was in the Army, doing a jump in North Carolina, and her chutes failed to open.  She targeted a pile of hay, and survived.
The terminal velocity of the human body is about 120 MPH, and may be less if the jumper can increase their drag. Picking the right landing spot, such as soft vegetation, appears to increase survivability. Landing in water seems to cause complications with breathing and also with the ability to swim if limbs are broken or consciousness is lost.
A co-worker was a base commander when a F-4 went down and the pilot's chute failed to deploy in the North Sea at night.  The pilot survived, and his injuries were limited to compressed discs and hypothermia. It took them about 70 minutes to fish out the pilot.
I do not know what the statistics are for water landings vs land landings, but it is generally recognized that a land touchdown provides more opportunity to steer to favorable soft targets.
Addendum:  This fall (2020), I met an Army ranger who had a chute and backup fail on a jump.  He targeted a pine tree, and tried to hit close to the trunk at the top.  He was scratched up and bruised, but walked out.  His situation happened 5 years ago in Northern Michigan. He has given several talks on it, but I have not located any video's.

"Landing in water seems to cause complications with breathing..." Excellent!!

While water displaces nicely at swimming displacement velocities, it does have about the same inertial mass as the body striking it, and there is further displacement resistance. So a body traveling at 120 MPH hitting water meets an effective mass with greater net force than if it just met a similar piece of jelly (water) in free air which could deform and spread with only the resistance and inertial properties of air.  Instead it has the inertial properties of the water around it, and the compressibility of water, rather than air.  Bottom line, it's a bigger ouch.

I'd have thought trying to aim for a tree or forrest type of area would be better than land or sea?

@mickburkejnr Well, you'll generally find more trees and forests on land than on water. Ergo, first step is to aim towards land instead of water (in case e.g. you are above water and can't make out features in the landscape, it's best to get closer to the land before trying to aim for a specific spot on the land).

I can back up the "pinetree theory": a person I know had a double failure of chutes about 20 years back. Luckily the airfield was surrounded by thickish pine tree forrest, and as it happened, the lucky bastard was fell through treetops onto a soft moss bed. You be your bottom dollar the terrified frieds did not believe what they saw when they rushed towards the "crash site", and the victim walked out of the forest with own two feet... I do not recall that the choice of landingsite was deliberate. I kinda have a hard time believing one would be able to aim too good at terminal velocity...

...so to aim close to tree trunk is a loooong shot, better just aim for the forest and hope for the best. The thing with pine branches is, that they crack rather easily, absorbing energy. Even in the case of pines hitting a thick, sturdy branch would definitely kill you, so very close to trunk would be fatal. Smaller branches you just pick up on your way down, losing your speed as momentum shifts to the branches and is lost into snapping them. Best case scenario - you accumulate a pine branch cushion on your way down

An impact on land has a small chance of survival, an impact on unbroken water has none.
Falling from thousands of feet without a parachute is very likely a death sentence, but there are a handful of cases in which people have survived. In nearly all of them, it is because the person landed in particularly hospitable terrain, like hitting a number of branches on the way down to slow their fall, or rolling down a steep hill.
All of these stories have one thing in common: slowly breaking your fall
What kills you isn't really the impact, it's the deceleration of the impact. You could be slowly lowered from 10,000 feet by a crane and you'd be just fine. But when you fall from great height, you build up a lot of speed as energy that has to be dissipated upon impact, and if it can't be dissipated into your environment it gets dissipated into you.
Your body can absorb reasonable impacts from reasonable heights, but it has limits. When you slowly break your fall, you're essentially splitting one unsurvivable impact into many smaller survivable ones.
What does this all have to do with land versus water?
Land has terrain. Water doesn't. If you hit the side of a grassy hill and roll down hundreds of feet before finally stopping, you've dissipated all this energy into the hill, while splitting up all the impact on your body.
If you hit the water, it really doesn't matter whether it's hot water, cold water, saltwater, freshwater, mineral water, branded water. It's going to be a very, very hard impact, and it's going to be head-on, because water is always level to gravity, so no hills or angles to dissipate energy. Water's very high surface tension means that at speed, the surface of water behaves much like the surface of a brick.
In Short:
Avoid water if you're falling without a parachute. Aim for trees. Or hills. Or peat bogs. Or giant trampolines. Or something that isn't flat and uniform like water.

It is not surface tension that causes the surface of the water to behave like a brick, it is the quasi-incompressibility of water. The body hitting the water will generate a large pressure at the impact point, but the water itself won't compress to absorb the shock. Surface tension force, which scales as $$gamma/R$$ where R is the radius of curvature and $\gamma$ the surface tension of a fluid, has nothing to do with it since the radius of curvature of a flat surface is, by definition, infinite

@BlaB Interesting. Feel free to edit my answer with the extra information :)

If you hit water with substantial numbers of air bubbles in it, you get much the same cushioning effect as if you'd hit a tree or a haystack.  Of course, conveniently-placed waterfalls or swimming pools filled with seltzer water are significantly less common than conveniently-placed forests...

"...slowly lowered from 10,000 feet by a crane and you'd be just fine if you didn't suffocate on your way down."  There's plenty of oxygen for survival at 10k feet.

@Mark I did think of that haha. That's the exact reason I said "branded water" instead of "seltzer water". I've heard a trip down Niagara Falls is surprisingly survivable because of how aerated the water is, though as you mention, not very common in the grand scheme of Earth's bodies of water

@WayneConrad Another great point. Feel free to edit that '10,000 feet' to '35,000 feet', which is more accurate anyway for falls from a commercial airliner at cruise altitude

@BlaB to Incompressibility I would also add density.

That suggests heavy waves might be at least somewhat better than still water, if suitable land isn't available. So, given the choice between open ocean and protected harbor, that favors the ocean.

@Novelocrat if you do survive, heavy waves may make it unlikely to be for long.

Nitpick: water is always level to gravity, so no hills or angles to dissipate energy, ever. Waves.  They might not be any help, but they exist and aren't level

What if it's soft water instead of hard water? :P

How? Just how the hell? If I landed on the water feet first? Are you telling a needle with enough attached weight to fall at the same speed or higher would hit the water and and break in two or bend without penetrating at impact? I find this very hard to believe. I'm landing on water.

@Seph We'll send our condolences.

At a freefall speed of 120MPH, water would provide a drag of about 1000 Gs which would be the same as hitting the ground and stopping in 6 inches (15cm). Better than concrete but still not survivable.

If you see a large water body around you, direct yourself to that.
Carry something which can cause a large concussive force just as you're about to impact. Say you're about to hit the water, you lob in object X which causes a large boom. The concussive force of the blast pushes you back and cushions you using the water as a "sofa" of sorts. You have to time this perfectly though, too soon and you miss it, too late and you get caught in it yourself. You can always try practicing by jumping from a low enough bridge into the water and trying, have enough health insurance and you'll be fine.

A "lob" of an object toward the ground while falling at terminal velocity seems somewhat difficult to achieve.

Didn't Mythbusters do this in 2003?    https://en.wikipedia.org/wiki/MythBusters_(2003_season)#Hammer_Bridge_Drop  Yes, yes they did.

Its also covered in this question on Worldbuilding    https://worldbuilding.stackexchange.com/questions/15661/

@Criggie According to the linked description, the mythbusters episode was throwing a hammer at the water to "break the surface tension" rather than throwing an explosive at the water and using the blast force to provide extra drag. In theory, causing the air to move rapidly upward a bit before you hit the water would indeed slow you down. Of course, you will run into the problem that Ken mentions: the object you throw down won't be moving downward much faster than you are, so it's quite likely to explode right beside you and reduce, not increase, your chances of survival.

@reirab Besides, what's the chance you're carrying a suitable explosive when your chute fails, you can reach for it in time AND happen to get the timing just right? Stick to land, water is deadly.

I do consider this answer dangerous. What's the consensus on dangerous answers, should they be flagged for removal?

@Mast It seems borderline ironic. I'm not sure the OP is really serious about it or it is just joking.

@Mast I take it as more of a joke than being serious. Maybe I'm just too optimistic or am underestimating how dumb people can be, but I don't think there's too much risk of someone reading this answer and then trying this.

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What are the requirements for grass height around runways and taxiways?
I am looking for the requirements for grass heights around runway and taxiway edges, signs and lights?

Do you have a specific country in mind?


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How does rudder size influence its ability to produce lateral lift?
Does anyone know how the area, height and width of a rudder affect how well it provides lateral lift? I've heard that the most effective rudders are around 35% of the vertical stabiliser MAC but is there any maths to back this up?

Its efficiency relative to its ability to provide lateral lift. I'm wondering if the area of the rudder control surface is increased, would that allow it to provide greater lateral force?

"the most effective rudders are around 35% of the vertical stabiliser MAC", that could be me, but I don't understand what it means. The "effectiveness" seems to be defined by the moment generated related to the CG vs. the angle of deflection, and in that case the effectiveness has no limit, the larger the area, the better the effectiveness. It also depends on the distance to the CG. Or do you mean moment generated vs. force applied to the rudder? It still depends on the distance.

The figure of 35% might be ideal for a rudder on GA aircraft with decent effectiveness and high enough control forces so a good control feel is achieved.
Generally, a rudder on a vertical tail is like a flap on a wing. It changes both camber and incidence of the vertical when deflected, thus helping the pilot to adjust the lateral lift force acting on the whole vertical. Therefore, the same formulas as those for flaps can be used for rudders.
A simple approximation for the amount of lift coefficient change per flap deflection angle $\eta$ is
$$c_{l\eta} = \sqrt{\lambda}\cdot\eta$$
where $\lambda$ is the relative chord of the flap and $\eta$ needs to be in radians.
Hermann Glauert derived a formula using potential flow theory that is sligthly more complex:
$$c_{l\eta} = c_{l\alpha}\cdot\frac{2}{\pi}\cdot\left(\sqrt{\lambda\cdot(1-\lambda)}+arcsin\sqrt{\lambda}\right)$$

I plotted both together with a correction of the Glauert formula using wind tunnel data above. It is remarkable how close the simple formula matches the experimental data already.
To be effective, the control forces on a rudder must not be too high, but also not too low in order to give good feedback to the pilot. For GA aircraft and gliders, a relative chord of 25 - 35% has been found to give the best combination. Control forces grow with the square of the relative chord of their control surface since both their area and the lever arm of the additional forces acting on them grow linearly with their relative chord.
In order to calculate the lateral lift change of the whole vertical, you need to know its lift curve slope $c_{l\alpha}$ which is affected by its aspect ratio and sweep angle, just like a wing is.

what is lambda_k?

@MatsLind The relative chord of the flap. 0.2 would be the value for a 20% flap.

Thanks! I was thinking that was lambda? What is lambda (without subscript) then?

@MatsLind: Small lambda is used for taper ratio. I admit, in this answer I was sloppy and used lambda without subscript for relative flap chord and then with subscript for the same thing.


text:
How common are emergency landings for airliners? Is there really more than one per day at Heathrow?
I've just found an article on one of Italy's most popular newspapers, the "Corriere della Sera", which states that emergency landings are far more common than is normally believed: according to it, at Heathrow there's at least one emergency landing per day. I find this number incredibly high. Is that true?
The article (which is more a collection of "quick facts") doesn't specify the source. I've turned to Google for further info, and the only result I've found is an article by The Telegrpah, which states that the average at Heathrow is slightly above one per week. Even assuming the Corriere journalist wanted to report that figure but got confused and accidentally wrote one per day instead of one per week, it still sounds very high.
An article on abc7ny.com (no idea how reputable that site is) mentions 66 emergency landings at JFK, 50 at Newark and 34 at LaGuardia over a 20-weeks span, from February to June of 2011.
On the other hand, the answers to these two questions on Quora indicate that emergency landings are very rare.
So, if we only consider airliners, how common are emergency landings really?
As pointed out by UnrecognizedFallingObject in a comment, it depends on what is meant by "emergency landing". Is there a commonly accepted definition? If not, since we have to draw a line, I'd say a Mayday counts for sure, and I'd also include a Pan-Pan. Below that, I think we can ignore it.

What is your definition of "emergency landing"?  Are you talking about something that's a declared Mayday, or something that encompasses both Mayday and Pan-Pan, or something narrower than a declared emergency even?

@UnrecognizedFallingObject Good point, I have edited my question.

@UnrecognizedFallingObject No expert but it's my understanding that Mayday/Pan-Pan are used on radio to attract attention to a distress call. For aviation when they already have the controllers ear, they simply say something like "we have an emergency". This is a declaration of emergency. True story: Plane already diverted to alternate in snow storm. Pilot says low fuel. Controller says either declare emergency or wait in line. Pilot declares emergency.

@D_Bester -- yes, that can happen.  The reason I distinguish between "Mayday" and "Pan-Pan" is because they're different levels of emergency if you will -- a "Mayday" situation is something is imperiling the flight now (such as being dead-stick, having primary flight control trouble, or getting smoked out of the cockpit so to speak), whereas a "Pan-Pan" is something that could be a problem, but isn't an immediate threat to flight (like stuck flaps).

A better definition would be, anything that is classified as being in the Alert Phase (ALERFA) or Distress Phase (DETRESFA). However, you are unlikely to actually find any such classifications of incidents in public material. I suggest you have a look here also: http://avherald.com/h?search_term=heathrow&opt=0&dosearch=1&search.x=0&search.y=0

One common emergency that can explain high numbers of "emergency"  landing is a passenger being sick. The flight safety was never endangered, but you still need to get the passenger out to get medical treatment.

iow if you count anything that calls for a diversion or return to base, 5 is quite likely. If you count only things the average person calls an emergency landing (iow the aircraft is about to fall out of the sky) I'd be surprised if it's as many as a few per year.

A lot of emergency landings (perhaps the majority but I have no sources) are "precautionary".  For example, an unsafe landing gear indication would be an emergency but normally, these problems are with the indicators, not the gear itself and the landing is a non-event, other than having the emergency services standby and a statistic having one added to it.

Do we consider all the toilets are blocked, we need to divert an emergency?

@Jamiec No. Or at least I wouldn't. It would be an unexpected event, but not an emergency.

@FabioTurati well the pilot of that flights seems to disagree with you.

I had my FR24 app set to alert on all 7700 squawks this summer. Just added up the numbers. In June there were 40 worldwide. In July there were 64. From Aug 10-31 there were 38. If you go by that there are a couple a day on average worldwide. That's just the ones that declared emergency and changed their transponder, though

@Jamiec, the pilot of that flight almost certainly did not consider it emergency either. There are many technical or operational reasons that require diversion and are not emergencies and this is one of them.

AAIB should have some bulletin on its web that lists reported incidents in UK and, speaking of Heathrow, it should be representative. However, there is one kind of emergency that will be hard to asses: medical emergency. This happens when somebody (except pilot; incapacitated pilot is normal emergency) on board becomes ill and needs prompt medical treatment. It would be considered emergency by layperson, but it is not a reported incident.

No, there isn't more than one emergency landing at Heathrow per day
The UK Air Accident Investigation Board (AAIB) defines serious (reportable) incidents in Appendix A of this document.  If we assume that an 'emergency' landing is one caused by one of the incidents in the list, then we can examine the AAIB reports to determine the number of emergency landings at Heathrow (the site supports filters).
I could only find three incidents reported at Heathrow in 2015:

27 July 2015 Airbus A320-232, G-EUYE - In flight fumes
5 February 2015 Airbus A330-323, N273AY - Collided with airbridge
6 March 2015 Boeing 777-236, G-RAES - Air turnback due to flight crew feeling unwell

Only two of these involved an 'emergency' landing.  2015 may not be a typical year, but a cursory check of the reports for 2014 and 2016 to-date suggests that there are very few incidents.
If you want to get a feel for the number of airline incidents and accidents each day, take a look at AVHerald (you might want to make a contribution to Simon's running costs).  That site reports 29 landings at Heathrow after accidents or incidents, of varying seriousness.  You'll see that, of the thousands of flights each day, there aren't that many problems reported.

Going with a much broader definition of "emergency landing", my local fire department gets called out "just in case" about once a month, or roughly one time for every 2000 aircraft movements.  Scaling that up to London Heathrow's 474,963 movements in 2016, and you'd expect to see emergency services staging about 238 times a year.  It's not quite daily, but it's not far from it.
Note that most of these are non-events: a bird strike that did no damage, or a faulty door sensor, or a funny odor in the cabin.  Maybe a few times a year, you'll see something that rises to the level of "incident": a failed hydraulic system, or an in-flight engine shutdown, or a pressurization failure.


text:
Is there a rule of thumb to choose an aircraft for long-haul operations?
Are there any rule of thumb for a  NEW commercial airliner, maybe 200 seater or more, for long-haul operations ? I imagine it would be -

mostly bigger aircraft as amount of fuel needed would be more
amount of food needed would be more
amount of waste generated would be more
discounts offered by manufacturer

all of which points to having bigger aircraft.
Apart from approximating number of passengers either between A or B or A - hub what sort of other factors influence what sort of aircraft would it be.
I am using long-haul definition from Wikipedia
To make it more precise - 200 or more pax.

This is almost impossible to answer as it greatly depends on the "mission". For example, a long-haul flight with 10 pax needs a very different aircraft than the same flight with 300 pax. Maybe there are no pax at all and it is cargo, then it depends on the weight and size. Typically airlines try to maximize benefits by cramming aircraft full of people and not fly empty aircraft. I think the biggest factor in estimating is historical trends and available equipment, not immediate needs.

@RonBeyer updated my query.

Because airplanes are incredibly expensive, using a "rule of thumb" would be extremely foolhardy.
A detailed analysis, likely laid out on a spreadsheet, would be much more appropriate.  You did hit on many of the major points, which also include:

Aircraft Range
Passenger Capacity
Speed
Crew Costs
Fuel Consumption
Cost per hour
Other costs: Insurance, Maintenance, and Leasing
Runway and Weight limitations
FBO services available

Obviously, if a candidate plane cannot fly the desired distance (perhaps limited by range, ETOPS, altitude or runway at takeoff or arrival), then you can't use that plane.  If a candidate plane cannot carry enough pax or cargo, then cross that off.
But once you have planes that can actually complete the mission, then its down to a complex matrix of costs, speed, time, and other benefits, and is a maximization problem without a precise answer.  (Some people will value speed above all else.  Some will value comfort and amenities.)

while you shared and are close, I updated the query to add 200 passengers at least or more pax. For such kind of scenario what kind of aircraft would be looked at ? I am not talking about specific models, but what sort of aircraft, wide-bodied, narrow-bodied, what would work in a  likely scenario.

As far as I'm aware, the only planes that can hold 200 people are Boeing and Airbus (737 and bigger for Boeing, all except the A319 / A320 for Airbus).  I do not know of any Embraer, Bombardier, or other major manufacturer that can hold 200+ pax.

@abelenky: Technically, the Il-96 would also qualify, but would be an odd choice. If upfront cost would be important, it would even have a fair chance.


text:
Does runway center lighting increase runway lifetime?
I wonder if the centerline lighting helps add a few more years to the runway, especially with heavy aircraft like A350/A380, in addition of being helpful for landing and takeoff?

My question is based on a recent reading where this question was asked:

Why did the airport operator BIAL not plan for centre line lighting
  at the time of runway construction?

Update - From what little I garnered, understood and logic applied, it seems/feels that a centre line lightning would make when the airplane lands with more precision than otherwise. This would mean that the aircraft doesn't go all over the place and while some specific parts of the runaway would be more stressed, others wouldn't. I know there are a mixture of narrow and wide-body aircraft but still it should make life of the runaway, at least on the edges more. Also maintenance of the runaway should be a tad easier as perhaps only some specific parts of the runaway would need more maintenance . I may be totally off in my assessment hence asking here.
Update 2 - From the comments then, what is the centreline lightning useful for ? Also if there any pictures which explains it as well would be useful. I know there are lights on left and right of the aircraft for it to know that there is a runaway here. What does centreline lightning bring to the table ?

The question seems to make most sense to me if one of the works planned for the runway closure the author complains about is installation of centerline lights -- even though it doesn't say so anywhere else in the article.

It depends on what you mean by lifetime. Lighting does not increase the strenght of runway. Lighting can help if higher catergory of operation is required. Lighting may not be installed from the start because there is no need to do so. So which aspect of lifetime you need to know?

My reading of that article is that the runway had to be closed in 2012 for surface repairs and will be closed again in 2017 to add lighting, but there's no link mentioned between the two issues.

@mins I updated my query, maybe you can shed some more light on the subject.

My raw assumption would be that general weather conditions(airport's climate) and traffic volumes would be the top factors by far.

No, runway centreline lights do not increase runway lifetime, and it is not their purpose to do so.


text:
Are airlines responsible for Airport security or Airports concerned or third-parties on terminal-side?
In Indian Airports, all sort of terminal-side security is done by CISF . They do all the frisking and baggage screening etc. I am concerned more for the terminal-side security rather than airside where it comes under the airlines domain.
Is it similar in the rest of the world or are airlines responsible? Some notable incidents I recall are the recent Brussels Airport attack, and the 2015 Sabiha Gökçen Airport bombing. I would suspect most airports now are under some sort of integrated command and control center modeled on the American system after 9/11 rather than have disparate silo-based security which may have holes that both terrorists and criminals may be able to get through.
I am talking from port of departure, where the procedure is, show tickets, passport at the main gate, go through security check, get boarding pass and board the plane.
Similarly, while de-planing, you go through customs and immigration, security check, baggage inspection etc.
At both places, security check is apparently done. My question is who is responsible, either the Airport Operator or the Government or a multitude of authorities ?
I am trying to be as generic as possible so as to know if there are variances or are most Airports following some set conventions ?
There have been many articles about TSA high-handedness but guess that's to be expected.

After the 9/11 hijackings/attacks, the US passed laws mandating that airport security screening be performed by Federal employees (i.e. the Transportation Security Administration, TSA). Wiki link
The Airport is required to provide the facilities to allow the screening process and be designed so that you can't slip past it. The Federal government pays the TSA staff, but Airports can also pay for private security, provided it meets Federal regulations and the TSA approves the plan. This is part of the Aviation and Transportation Security Act.
See this document for a lot of information on the subject:

Section 108 established the Security Screening Opt-Out Program, whereby an airport could petition the TSA for private security screeners. This program was complemented and supported by the Pilot Program, which would develop policies and procedures for private screeners and would also provide real world experience for private screener activity.

As of 2015 it appears that just over 20 airports had privately contracted security

In its June 2015 report to Congress, the Transportation Security Administration summarized the current status of the Screening Partnership Program as follows: “Since the creation of the program in 2004, 32 airports have applied to the program. Of the 32 airports, 27 airports were approved, 3 airports retracted their application, and 2 airports were denied and have not since reapplied to the program. Currently, 21 airports are participating in the program with contract security screeners in place. Additionally, TSA is in the procurement stage for one new airport. Currently no applications are pending approval.”

In the United States of America passenger and baggage screening is handled by the Transportation Security Administration (TSA). It is a government run agency and deals with the pat downs, X-Ray machines and frisks. This will get you through "security" and to the terminal area and ultimately on to the plane.
If you are coming in from another country you will need to pass through customs which is managed by its own agents and falls under the jurisdiction of U.S. Customs and Border Patrol who are also a federal agency.
At some of the really busy airports here in the US its not uncommon to see local police officers helping out with things like traffic flow and passenger management of those entering and exiting the facility and security in general.

Another reason to have police at the airport: TSA can't arrest you - the police can. https://www.tsa.gov/blog/2016/07/03/tsa-myth-busters-do-tsa-officers-arrest-passengers

I can attest that the police are present at FRA/EDDF! After having my bag somehow test positive for explosives (after having already been screened at ORD), I had a friendly chat with several of the local Polizei while the security guy went through everything with a fine tooth comb.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What was the airline attendants looking at in LED display before light off in A320
I was journeying on Indigo Pune-COK back and forth. At both the times, I noticed airline attedants looking at some LED display which seemed to be some sort of balance scale. At first, I thought they might be looking to check at some sort of weight distribution sensor to check whether things are distributed evenly all across the aircraft or something else. I am not sure now but would be glad if somebody could chime in. The plane is and was single class 180 Airbus A320. https://seatguru.com/airlines/IndiGo/IndiGo_Airbus_A320.php
Edit : Update - . Both times, it was before the takeoff procedure. The LED/LCD display was located above the flight attendants chair on the left . The chair on which they sit in the front during take off. The one which is located to left of the refreshments and just before the pilot cabin/cockpit.  The LED/LCD display was above the flight attendant's chair at eye-level.
While I'm sure it had to do with probably some sort of avionics controls they were looking at, I am not sure what.

Can you add some more details? At what point before/during/after the flight did you see this? Where exactly was the display located in the aircraft?

@Pondlife I edited and updated the question with bit more specifics, does that give some additional idea/info ?

Possible duplicate of What can the Flight Attendant Panel do?

The panel you have seen near the forward left door was most probably the Flight Attendant Panel of the CIDS (Cabin Intercommunication Data System). It looks like this: picture of the CIDS panel at jetphotos.com
In the lower part, it has two LED scales which can show the quantities in the fresh and waste water tanks of the aircraft. If I remember correctly, they will only light up while the IND ON pushbutton next to them is pressed.
The cabin crew will routinely check those water levels to ensure e.g. the lavatories can be used.

solves my question, thank you.


text:
Do I have to declare an emergency if I cut into fuel reserves?
In another question, I wrote

You only need to plan for regulatory reserves. You don't actually have to land with them

and @Jan replied:

you have to declare emergency if you do cut into them though and that will quite probably get you an investigation

I have never heard that you must declare an emergency if you cut into your reserves (regardless of the stage of flight), and I'm wondering if there is any regulation to back it up.
The only reg that I could find that comes close is NTSB 830, which lists a set of criteria for notifying the NTSB within 10 days:

(a) An aircraft accident or any of the following listed serious incidents occur:
(1) Flight control system malfunction or failure;
(2) Inability of any required flight crew member to perform normal flight duties as a result of injury or illness;
(3) Failure of any internal turbine engine component that results in the escape of debris other than out the exhaust path;
(4) In-flight fire;
(5) Aircraft collision in flight;
(6) Damage to property, other than the aircraft, estimated to exceed $25,000 for repair (including materials and labor) or fair market value in the event of total loss, whichever is less.
(7) For large multiengine aircraft (more than 12,500 pounds maximum certificated takeoff weight): (a bunch of other things)

I'm interested in the answer for Parts 91, 135, and 121, under FAA regulations.

if you cut into your reserves while lining up for the runway it's not useful to declare fuel shortage. If you miss the approach then it is useful to get the priority the emergency gives you.

I am not aware of anything that would require you to declare an emergency for fuel reserves. For that matter, I'm not aware of anything that would require you, strictly speaking, to declare an emergency in any circumstance.

Speaking from the standpoint of one who retired in 1999, if I had declared a fuel emergency every time I cut into the 45 minute reserve normally required back then for an IFR reserve, I would have been declaring an emergency on a regular basis. A fuel emergency, at least back then, was declared only if you thought you were going to run out of fuel if you didn't get priority handling. I never declared such, and to the best of my knowledge, I never landed without enough fuel to do a go-around and then circuit the field for a landing.

I don't think it's regulation but I do believe some airlines have the SOP to declare emergency if you can no longer make the runway without cutting into your reserves. I have no source for that though.

My PPL instructor told me that its not necessarily an emergency, but you better have a good explanation ready if you get ramp checked. Declaring an emergency is always a judgement call by the pilot, if you feel that you need extra resources or attention to get your aircraft safely on the ground, then declare. Otherwise you can always use the Aviation Safety Reporting System (ASRS) and be somewhat covered if somebody at the FBO reports you.

In the US, FAR 121.557(c) requires the pilot to inform ATC any time they "excercise emergency authority".  I'm not a Part 121 pilot and am not well versed on Part 121 procedures, but I don't think that eating into reserve fuel qualifies as an emergency.
The relevant similar regulation in Part 91 is 91.3.  It requires pilots who deviate from the FARs to file a report on request of the FAA, but notably does not require a pilot to ever declare an emergency.

@ratchetfreak I had to read that twice before I realized it wasn't talking about lining up for the runway on the ground.

There seems to be no regulations that require decleration of emergency in case of using reserve fuel. US DoT InFO 8004 specifically discusses this:

Emergency Fuel. Although not defined in the AIM or Federal aviation regulations, the  industry-wide connotation typically associated with the
  term “Fuel Emergency” is:
The point at which, in the judgment of the pilot-in-command, it is necessary to proceed directly to the airport of in tended landing due to low fuel. Declaration of a fuel emergency is an explicit statement that priority handling by ATC is both required and expected.

Noting that pilot declaring minimum fuel is not an emergency,

The act of using a portion of the reserve fuel assigned to a flight is not,  in its self a cause to declare a minimum fuel state with the controlling agency. Regulations require reserve fuel to enable aircraft to maneuver, due to unforeseen circumstances. Many aircraft safely arrive at their destination having used a portion of the fuel designated as reserve. There is no regulatory definition as to when, specifically, a pilot must  declare “minimum fuel” or a fuel emergency. Air carriers typically develop such guidance for their pilots and include it in their General Operations
  Manuals; such guidance generally  falls along the following lines:
•Declare “minimum fuel” when, in your best judgment, any additional delay will cause you to burn into your reserve fuel.
•Declare a fuel emergency at the point at which, in your judgment, it is necessary for you to proceed directly to the airport at which you intend to land. Declaration of a fuel emergency is an explicit statement that priority handling by ATC is necessary and expected.

(Emphasis mine)

No, you don't, but per the AIM you should declare an emergency if you need priority for landing.
There may be some confusion here between declaring "minimum fuel" to ATC, and declaring an emergency. The AIM 5-5-15 says:

Advise ATC of your minimum fuel status when your fuel supply has reached a state where, upon reaching destination, you cannot accept
  any undue delay.
Be aware this is not an emergency situation, but merely an advisory that indicates an emergency situation is possible should any undue
  delay occur.

[...]

If the remaining usable fuel supply suggests the need for traffic priority to ensure a safe landing, you should declare an emergency due
  to low fuel and report fuel remaining in minutes.

But in general there's no regulation or rule that I can find that says when a pilot must declare an emergency. The general guidance from the AIM 6-1-2 is that pilots are expected to declare an emergency when a state of distress exists. The ATC orders 10-1-1 are a little more specific:

A pilot who encounters a Distress condition should declare an
  emergency by beginning the initial communication with the word
  “Mayday,” preferably repeated three times. For an Urgency condition,
  the word “Pan-Pan” should be used in the same manner.

As for what distress actually means, the Pilot/Controller Glossary simply says:

DISTRESS− A condition of being threatened by serious and/or imminent
  danger and of requiring immediate assistance.

It's unlikely that cutting into fuel reserves by itself would constitute a "serious or imminent danger" (which is why "minimum fuel" isn't an emergency) but on the other hand if the pilot is also unsure of his position or has other issues to deal with, then it might still be the best thing to do.

One time after WX and extended vectors (over 50 minutes of additional delay), I was almost ready to cut into my night IFR with alternate reserves plus my modest buffer.  Not the legal minimum, but my minimum.  I told Baltimore Approach that I was declaring "MINIMUM FUEL." I was asked how much fuel I hand on board, which I provided in minutes. I was also asked for souls on board. They handed me to Dulles Approach, explaining that Dulles had better coverage for KGAI, even though KGAI was in their airspace (or sector).
My rules for the flight were that if I had any more delaying vectors I would have to divert, and given the WX, diversion would potentially be problematic.  I had been cleared to KGAI, but if I was delayed further I would have to land somewhere else.
To be clear, I did not intend to declare an emergency, but the controllers treated it that way.  Dulles gave me a dedicated controller and kid glove handling to KGAI, and cleared me for the NDB approach. He also called the FBO to verify I made it in, I was told by the line guy. The Dulles controller had asked me to call him when I landed, so I called Baltimore on Clearance Delivery, and asked them to tell Dulles I landed and appreciated the assistance.
It was raining hard, but I took the time to dip the tank, because I wanted to know exactly where I was fuel wise. I was within 1 gal of my estimated fuel, which was 1:45 plus unusable, as I was at night, IFR, and with weather that required an alternate.
There was never any paperwork.  The following week, when I got home, I sent both Baltimore and Dulles a thank you letter for their handling of things. To this day I use this flight as an example to students of the power of "MINIMUM FUEL."

In Australia, the answer is yes if you expect to land with less than the fixed fuel reserve. CASA 29/18 – Civil Aviation (Fuel Requirements) Instrument 2018 s7(5):

The pilot in command must declare a situation of emergency fuel when the calculated usable fuel predicted to be available upon landing at the nearest aerodrome where a safe landing can be made is less than the fixed fuel reserve for the flight. The pilot in command must declare an emergency fuel state by broadcasting MAYDAY, MAYDAY, MAYDAY FUEL.

https://www.legislation.gov.au/Details/F2018L00644/Html/Text#_Toc514142500

While this is interesting, since the question is specifically asking for answers relating to the regulatory situation in the US, I'm not sure it is actually an answer. Otherwise, one answer per regulatory region in the entire world would count as answers to every question involving regulations, which does not seem appropriate to me; it would quickly get extremely unwieldy, and would not be of much help to the person asking each respective question.

Fair to question whether it's an answer, but I took guidance from this meta-answer: https://aviation.meta.stackexchange.com/a/453/558 -- essentially, could the answer help other people who have arrived at the question? Since the question title is general, it's almost certain someone from a non-US jurisdiction will arrive at it, hoping for non-US answers.

Fair enough. I'd question that part of the reasoning in that meta answer, but that's not really a discussion for the comments here. Since it's been a few years and the site has matured a lot since that was posted, it might be worth revisiting the issue on Meta.

Wow, that's just bizarre.  "Mayday mayday mayday" just because you are going to cut into your planned reserve?


text:
Why does this GPS approach say "RADAR REQUIRED"?
As I was looking at the approach charts for KCXY while answering this question, I realized that the GPS "overlay-style" approach to RW8 also requires RADAR.
Since the HAR VOR isn't even shown on this Approach, and it has an IF, why should RADAR be required?
Note that the RNAV (GPS) RWY 26 approach to this airport does not require radar.

Possible duplicate of Why is radar required on some FAA instrument approaches?

I'm going to hazard a guess that it has to do with the close proximity of Harrisburg MDT. In a non-radar environment, an aircraft flying this approach would surely limit traffic being allowed to approach or depart MDT. Perhaps the RADAR requirement is to limit this approach to use when it would have a minimal impact on MDT traffic.

@abelenky its not a duplicate of that answer, and in fact, I reference that answer.

@JonathanWalters by that logic, every approach inside busy airspace would say "RADAR REQUIRED", which we know is not true.

No, that logic leads to exactly the sort of answer you give for your CAT II / III requirements below. Close proximity creating an impact on traffic for some reason.

your logic "in heavy traffic areas, RADAR is required to maintain separation" is falsifiable. Mine is not (yet).

here's an example of an approach under the SFO main approach path that doesn't require radar http://flightaware.com/resources/airport/SQL/IAP/RNAV+(GPS)+Y+RWY+30/pdf

Not heavy traffic, but close proximity, especially the intersecting approach departure areas. I don't think heavy traffic has anything to do with it. I don't know where you found your quote about heavy traffic.

i retract the word 'heavy'. the comment stands. nevertheless, you haven't provided any evidence, say AIM or TERPS.

Let us continue this discussion in chat.

The immediate reason seems to be that for RNAV approaches that start at an IF (Intermediate Fix) - not an IAF (Initial Approach Fix) - radar is required per the ATC orders (4-8-1h):

issue approach clearance [...] only after the aircraft is:

Established on a heading or course direct to the IF at an angle not greater than 90 degrees, provided the following conditions are met:

[...]
(b) Radar monitoring is provided to the IF.
  (c) The SIAP must identify the intermediate fix with the letters “IF.”

The RNAV 26 approach that you mentioned does have an IAF, so according to the same rules radar isn't always required for it.
You might now ask, why is radar required for RNAV approaches that start at an IF? Because, it doesn't have an IAF.
The next question is why doesn't it have an IAF? Probably because of higher terrain north of the approach corridor? Or maybe (as per @Jonathan Walter's answer) there is sufficient Radar coverage to vector to the IF, so it doesn't need an IAF.

yes, thanks, you found it. There's no way to begin the approach without radar if there's no IAF, as per http://blog.aopa.org/opinionleaders/tag/intermediate-fix/


text:
Why does the speed of commercial airliners fluctuate, sometimes as high as 1,060 km/h or as low as 800 km/h?
I've noticed that (long-haul) airliners sometimes travel at as high as 1000  km/h (I believe I've even seen 1040 km/h), but usually they fly closer to 800 km/h, for most of the trip.  This seems odd to me.
I would understand this if it was due to wind speed; however, usually those that travel slowly seem to do so for most if not all of the journey, regardless of the direction of travel (e.g. even if they are going up to the north pole and back down, and whether the net direction is west or east). I find it nearly impossible to explain this using wind speed.
Similarly, given that the speed of sound is around 1,060 km/h at 12 km above sea level, I find it equally uncompelling to reason that they need to go at less than mach 0.8 due to the speed of sound. I would understand it if they limited themselves to (say) mach 0.95 (obviously you don't want to do mach 0.99 due to variability etc.), but I routinely see top speeds that are around mach 0.8 for cross-continental flights, and I don't understand why.
So, what's the real reason?

AFAIK the 747 is still the fastest airliner in service at 0.85 Mach. Even at 0.8 M some parts of the aircraft experience supersonic flow.

BTW, where are you seeing these speeds?

@TomMcW: Oh interesting. I'm seeing them on the monitors in the cabin.

@ymb1 All the different speeds and Mach numbers can get really confusing. I still haven't figured out what Calibrated airspeed is used for.

Planes fly at about 800 km/h for the same reason you drive about 80 mph on the highway .. it is what they are designed to do.

@J.Hougaard: Wait, who says I drive 80 mph on the highway!? =P

You see M.8 routinely because that's the cruise value for many airliners (that's a "speed" related to air). You see varying speed displayed to the public because this is a speed related to ground which depends on winds. While Mach number is used to fly the aircraft, the trip time depends only on the ground speed. M.8 and not M.95 because in the transonic segment (M.85 to M1.2) there is a mix of subsonic and supersonic flows requiring different designs to be effective (delta-like wings for instance). This additional cost is not commercially viable.

Related question: http://aviation.stackexchange.com/questions/11936/are-we-at-peak-speed-efficiency-for-jet-airliners-at-mach-0-85

This is not duplicate of the marked question. That question is about what the top speed is, but this one is about why it is sometimes indicated as high as 1,060 km/h and sometimes as low as 800 km/h, which that one does not even touch.

@JanHudec if the question is really "about why it is sometimes indicated as high as 1,060 km/h and sometimes as low as 800 km/h" I think it needs adjustments, for how I read it, it is about "why they limit themselves to 0.8 Mach"

@Federico, why they limit themselves to 0.8 Mach is part of the question, but clearly the variation is part of it too and must be explained to answer it, even with the current wording. The suggested duplicate does not do that.

There are three different speeds that are of relevance here:

Groundspeed- This is probably the speed indicated to the passenger. For them, this is the most relevant as it determines the time taken for the trip
Airspeed- This is the speed of relevance to the flight crew and is used for flight.
Local airspeed- This determines the maximum speed of (subsonic) airliners. The reason is that the local airspeed over the wings are higher compared to the undisturbed flow- a result of the air being accelerated over the wing. As a result, the local airspeed over the wing can exceed Mach 1 quite a bit before the airspeed of the airliner goes anywhere near that.

The result of such local supersonic flow would be a rapid rise of drag at the drag divergence Mach number (which is greater than the critical Mach number).

Image taken from notes of Advanced Aerodynamics by Professor H.M. Atassi of University of Notre Dame
In order to avoid the drag penalty, the airliners fly at speeds below the drag divergence Mach number. The reason is reduced speed is not the free-stream Mach number- it is the local Mach number, which should be kept below the Drag divergence Mach number.

+1 so I guess the important point here is that even an airliner at Mach 0.8 probably has airflow somewhere near Mach 1... is that correct? (just checking, because it's more than I intuitively expected)

@Mehrdad Yes. Also remember that the Mach numbers depends on, e.g., umidity and temperature. so the same speed could be Mach 0.8 in a certain condition and Mach 0.95 in an other.

It is all about the wind. If you check schedules, you'll see that for example USA-Europe flights are way shorter (about an hour, say) than Europe -USA. This is due to the jetstream. I found it even more significant in the Southern hemisphere, when flying Australia-New Zealand (and back) or Santiago-Buenos Aires.
As mentioned in the other answers, no commercial jet goes anywhere near mach 1. The ground speed you are shown may be close to the speed of sound (it could even be higher, if the wind were strong enough), but the actual airspeed of the aircraft (its speed relative to the air mass) is way less than that (around mach 0.8 for the bigger jets, and less for many smaller comercial aircraft).

Similarly, given that the speed of sound is around 1,060 km/h at 12 km above sea level, I find it equally uncompelling to reason that they need to go at less than mach 0.8 due to the speed of sound. I would understand it if they limited themselves to (say) mach 0.95 (obviously you don't want to do mach 0.99 due to variability etc.), but I routinely see top speeds that are around mach 0.8 for cross-continental flights, and I don't understand why.

What matters is the speed of the air passing the plane. As the other answers have explained, the numbers you see in the cabin are typically speed over the ground, rather than speed through the air, so a big component of the difference is whether the plane has a headwind or a tailwind, which can easily add or subtract 100km/h at cruise altitude.
The other thing you need to look at is not just the plane's speed through the air but the speed of the airflow over the plane.  How are those things different? The point is that, as a plane pushes through a mass of air, air has to move out of the way of the big metal thing. This means that the air passing over the plane will be moving quite a bit faster than the plane's speed relative to the air. Thus, even a plane moving quite a bit below Mach 1 can have supersonic air flowing over it. The reason you don't fly at Mach 0.99 is not because a gust of headwind might take you over the speed of sound, but because you'd already be experiencing supersonic airflow  100% of the time, at that speed.

There are other factors that people already mentioned.
On modern jets the flight computer can be programmed for efficiency during the route.
One of the reasons why mach 0.6-0.8 is used is it is sufficiently fast without burning a lot more fuel. The 777 if I remember correctly uses about 30% more fuel fully loaded to accelerate to 0.87 (edited) mach than at 0.7 mach at around 11.5 km. That's a lot of fuel to save yourself less than 20% of time. That extra fuel would result in more expensive tickets, in an industry which is trying to keep ticket prices to the minimum to compete.

I don't think the last part of your answer makes any sense.


text:
What is the highest operational ceiling for a nuclear scramjet?
A similar question is:
What is the highest operational ceiling for an air-breathing jet engine?
The answers point to scramjets. Cited reports focus on combustion kinetics.
The Wikipedia Scramjet page:

a block of gas entering the combustion chamber must mix with fuel and
have sufficient time for initiation and reaction, all the while
traveling supersonically through the combustion chamber, before the
burned gas is expanded through the thrust nozzle. This places
stringent requirements on the pressure and temperature of the flow,
and requires that the fuel injection and mixing be extremely
efficient.

For a nuke, no combustion is needed. How does this change the altitude limit?
The document cited by mins 3 concludes that speed and altitude are limited by reactor wall temperature for a nuclear-powered, direct air, shield-less, ram-jet. Twall of 1800 Rankine enables flight at "70,000 feet and a flight Mach number of 3.0, a uranium investment of 81 pounds and a missile gross weight of 64,000 pounds." It goes on to say "lift-drag ratios as low as 3.5 could be tolerated. ... lift-to-drag ratio was estimated at about 5.0."
The nuclear-powered ramjet combines the conventional diffuser and exhaust nozzle with a nuclear reactor. The diffuser decelerates the free-stream air before it enters the reactor passages. Reactor inlet air Mach number is about 0.28.
The question then becomes, for a nuclear scramjet, where inlet air is not braked to subsonic speeds, what improvement in ceiling is attainable?
The conventional fuel-burning scramjet would be limited by the oxygen available at altitude. The nuke needs only atmospheric mass. There is plenty of air at 81,000 feet to provide the needed thrust, according to my amateur calcuations:
W = 64,000 lbf, L/D = 4, let L = W so W/D = 4
drag D = W/4 = 64,000/4 = 16,000 lbf
We need thrust T = D
T = mdot*(u - v) = (mass flow rate)(exhaust velocity - intake velocity)
For a nuclear thermal rocket Isp = 900 s = u/g,
so u = (900 s)(9.8 m/s2) = 8,820 m/s
let v = Mach 15 = 15(343 m/s) = 5,145 m/s
mdot = (atm density)(intake area)(velocity) = rhoAv
at 25,000 m = 81,000 ft, density rho = 0.04 kg/m3
let intake diameter = 3 m, so A about 7 m2
mdot = (0.04 kg/m3)(7 m2)(5,145 m/s) = 1,441 kg/s
T = mdot(u - v) = (1,441 kg/s)(8,820 - 5,145) m/s = 5.3 MN
T= (5,300,000 N)(0.2248 lbf/N) = 1,190,000 lbf

Determining the ceiling requires knowing not just the type of engine employed, but also knowing about the weight and aerodynamic characteristics of the aircraft.  Without such information, there is no way to give any answer.  VTC as needing far more detail about the hypothetical aircraft in order to be answerable.

@Ralph J: The related question and its answers do not include the aero or weight of the aircraft.

You may be interested in this document for missiles. The problem doesn't seem to be altitude, as for a payload of about 5 tons, it was possible to design a missile flying at 80,000 ft at Mach 3. The less air, the more the required air acceleration, and the hotter temperature for the heater.

The related question is also asking about existing aircraft - what is the highest ceiling of any existing aircraft. Since nuclear-powered aircraft have never flown, there is no empirical answer to their ceiling. Any answer here would either be speculation, or else it would reflect whatever assumptions are made regarding weight, thrust, and aerodynamics. If one assumes, or "fantasizes" might be a better description, a high enough thrust and a low enough weight and good enough aerodynamics, you can get amazing output... but it's all about data in, data out; or garbage in, garbage out.

I voted to reopen. The question is well formulated and focused. A theoretical maximum limit could be calculated based on pure engine performance, no other data needed (equivalent to saying that a piston engine cannot operate above X altidude because too low air density or whatever)

The paragraph that starts, "The document cited by mins..." seems to include one or more quotes and possibly more than one source. Would you please improve the formatting of that section, as it's unclear what is an actual quote from the linked document, what isn't a direct quote, and if there really is more than one source (or, perhaps, the quote includes a quote from another document).


text:
What exactly are Norways problems with the NH-90?
Several news sources (here, or here) report that Norway wants to terminate its contract with NH Industries and they want to return their delivered NH-90 helicopters. The citation goes as follows:
"“Regrettably we have reached the conclusion that no matter how many hours our technicians work, and how many parts we order, it will never make the NH90 capable of to meeting the requirements of the Norwegian Armed Forces."
What exactly are the requirements that the NH-90 is unable to reach? To clarify, I am interested in which exact technical details/requirements are violated that leads norway to conclude that "it will never make the NH90 capable of meeting the requirements"

Is this really on topic here?

The help center states: "Aviation Stack Exchange is a site for pilots, engineers, controllers, mechanics, and aviation enthusiasts. If you have a question about [...] Aircraft Design and Manufacture." I would argue that this is a question about the design (because of the requirements). Dont you agree?

No, I do not agree that this is a question about aircraft design, I really struggle to see how it can be seen in that perspective

Well I do ask about the exact set of requirements. I assumed that there are a quantifiable number of requirements which cannot be reached (e.g. Door too small, or landing gear fails). Perhaps you think that this question goes too much into politics? If so I would respond that obviously a certain political aspect is involved in the discussion, but I am interested in the exact technical reasons for rejecting the NH-90. Therefore to the best of my knowledge the question is not oppinion based and thus on topic. If I am mistaken, please indicate what the exact problem is.

if you really are interested only in the technical side of things, please specify as much in the question. also, specify the side of "technical". the answer that you got so far is technical, but as WPNSGuy says, it is nowhere close to be a "design" thing.

I tried to sharpen the question towards the exact technical details, but given that the questions jumps back and forth between 0, 1 and 2 upvotes, I think you might not be the only one who doubts the correctness of the question :D.

@U_flow - It appears to be a lack of flyable aircraft. The contract was for 14 airframes, capable of sustaining 3,900 flying hours annually. For whatever reason, it does not appear it can do that. Either too few airframes, or the ones they have are too maintenance intensive. "We've been screwing with these things for 20 years, and can't keep them in the air long enough. Cancel the contract, see ya goodbye."

@WPNSGuy Yes, but I wonder if there are similar capability deficiencies as australia identified for the Eurocopter Tiger: https://www.flightglobal.com/australian-government-auditor-slams-tiger-attack-helicopter/121607.article. I guess that my question entails if the low availability of the NH90 is the only deficiency identified or if there are also other reasons...

@U_flow - Why should there be similarities? Different manufacturers, different missions, different capabilities, different aircraft...completely different problems.

@WPNSGuy Well both are european helicopters, one manufactured by AHD and the other one partially manufactured by AHD. But I get your point. This must not necessarily mean that the same problem exists on the two helicopters, but I wanted to see if anyone had any further insights on this topic.

What exactly are the requirements that the NH-90 is unable to reach?

It appears delivery and availability. Not everything is a "design" issue.
It says right in your second link:

Norway’s acquisition of the NH90 began in 2001, with 14 helicopters for Coast Guard and Anti-Submarine Warfare duties originally slated for delivery by the end of 2008. As of today, only eight have been delivered in a fully operational configuration. The fleet is currently required to provide 3.900 flight hours annually but in recent years it has averaged only about 700 hours.

Over a decade late, only 8 of 14 aircraft contracted for, and only 700 of the required 3,900 annual flight hours.

In December 2021 Australia announced early retirement for its 47 NH90s, which entered service in 2014, blaming "unreliability” and cost.

If they have the same problems as the Dutch Navy, the helicopters are extremely unreliable and need far more than the originally estimated maintenance hours and waiting for spare parts.


text:
Does a public use aircraft need an aircraft registration hard card?
Does an aircraft, operating public use, need a aircraft registration hard card?

What jurisdiction are you asking about? FAA?

What is an "aircraft registration hard card"?

@FreeMan Google suggests its an FAA Form 8050-3.

If you are talking about the FAA and if you are talking about a physical registration card (certificate), then yes, as per FAR 91.203 a physical copy of the certificate is required on board the aircraft.

@RonBeyer Doesn't §91.203 apply to civil aircraft, not public aircraft?

Related


text:
What are the advantages of the Cri-Cri's tail and fuselage design?
I have some questions regarding the Cri-Cri design. If some of them can't be answered directly, I would like to read what theory says about it.

Why is a T-tail used? What are its advantages for an LSA over a classic tail?
The plane has a polygon-shaped fuselage which is not streamlined. How much efficiency was traded for production simplicity?

@SteveV. Hi Steve, I've cut the question. There are still two points in it, but probably they aren't worth opening separate post for each one. Hope this is ok.

I have the impression that your first question might be answered here: https://aviation.stackexchange.com/q/1400/1467 and as for the second question, "is it worth" begs the answer "it depends", as it in the end is a matter of opinions of the designer (and what were their design goals)

@Federico, thanks for the link. It certainly an opinion of the designer, but probably this was (or can be) explained, since the aircraft is in production for over four decades. In the second question I try to understand how to evaluate losses due to rigid forms.

The T-tail positions the horizontal stabilizer out of the turbulent "prop wash".  This reduces the strength and weight that would be required of the structure if it had to endure the aerodynamic stress behind the two propellers (which is terrific).
This simple shape has everything to do with parts and assembly simplicity and low cost for the homebuilder.  Drag increases exponentially with speed; so for slow aircraft, draggy shaped components are much less a problem.

Thank you, STWilson. Never thought downwash from these two small propellers would be so strong that it makes sense overhead for having reinforced tail structure. Regarding fuselage shape, is the "boat-like" shape really simplier to manufacture for a homebuilder than a conventional oval shape? What does make this difference?

Contored surfaces require stretch forming the skins to obtain a compound shape.  The skins in this design are not formed,  just cut and trim.

Turbulence aft the propellers would not be characterized as downwash.  Think of it as a spiraling mess to be avoided, very hard on airfoils (like stabilizers) behind it.  https://youtu.be/1z6M0NrDM2U?t=1m56s

Are skins carry any load in cri-cri (and likewise LSA)?

Yes, the skins are structural.  It's called a monocoque design.

Thank you for video and explanations!
How contored surfaces were manufactured in WW2-era?
What is the approximate speed at which fuselage's shape start to play its role? As I can judje on my car, border speed is about 140-160 km/h (90-100 mph), but Cri-Cri is much faster.

Stretch forming:  https://www.youtube.com/watch?v=Kh4MBHyHAtg.  @Eugene  I encourage you to join in the chats when the system grants you that privilege.  It's discouraged to carry on conversations here in the questions.  Good luck in your pursuits!


text:
How did KAL 007 get so far off course?
Regarding Flight 007 that got shot down in the Soviet Union, this was reported in the New York Times:
Study Says Korean Airliner Was on Its Intended Course When Downed in '83 (nytimes.com)
Excerpt:

A retired airline navigator has gathered evidence that in his view
  shows that the South Korean airliner shot down over Russia in 1983 was
  on a deliberate flight path and did not stray accidentally into Soviet
  territory.
A principal part of his analysis is his refutation of what has been
  the prevailing theory, that the plane unintentionally flew off course
  because of a single-digit mistake in keying flight coordinates into
  the navigation system.
Leading aviation officials accept the refutation as correct, but still
  insist that the incursion was accidental and not deliberate.

We know this was a modern (at the time) Boeing 747 with a complex inertial flight management system.

No, I do not believe the theories about this being intentional.  Nobody would risk a plane full of passengers like this on purpose.
In 1978 the KAL flight 978 went astray and was forced down on a frozen lake inside Russia.
Korean Air Lines jet forced down over Soviet Union - Apr 20, 1978 (history.com)
I would think this would be on their mind as they prepared for the flight.

So my question is:  How did KAL 007 get so far off course?
Follow-up:  Wouldn't they have noticed?

The NYTimes item you link to is an archival piece from 1992.  I don't believe that's the currently accepted idea (which is that the autopilot was incorrectly set to follow a compass heading and not the programmed waypoints).

Also, electronics and interfaces have changed considerably from 1983.  Modern airliners will have multiple changes in how they operate and are programmed compared to how it was done then.

The changes since then include GPS and all that, of course. I rode the first Alaska Airlines flight into Juneau that used GPS for landing. That was mid-90s.  I just happened to be on it.  And just happened to be sitting next to an AA manager.  We talked all about it.  Then, just before we landed a lady right in front of us pulled out her cellphone and made a call.  He just laughed and said not to worry about it.  It was a perfect landing.

The FMS was set properly.  They likely believed it was in use and working.  Unfortunately, it was not engaged.  More waypoints would not have helped.

Chapter 4 of Degani's Taming HAL covers some of the details of this disaster, and is on a NASA site The Crash of Korean Air
Lines Flight 007
It details some of the interface deficiencies in the aircraft's navigation selection system.  We don't have definitive evidence about exactly what happened, but it is possible.  It goes over the idea that it was easy to get the system in a mode where the pilots could easily have thought that the inertial navigation system was engaged, but actually wasn't.
The Mayday show covered this one as well.  They noted that after the FDR was returned, it showed that the FMS was set properly.  Even though it wasn't controlling the plane, it would have continued to show the waypoints being passed as the aircraft crossed to the side.  Given that behavior, it would be very easy to believe that the system is working and you're where you should be.

This makes a lot of sense.  So even if it was set properly it wouldn't have helped.  Accept.  Yet the question still lingers about why they didn't notice.

@SDsolar as humans we miss things all the time. They saw the indications that told them it was working, as it always did, and felt no reason to monitor more closely.

Good point.  You reminded me of JFK Jr.  He didn't trust his instruments and ended up in a death spiral.

The believed fate of Flight 007 is that the autopilot was set to fly the compass heading instead of the INS (source: revised ICAO report). As for the likelihood of incorrectly entering waypoints; the way the procedure works is that the Captain would say the waypoints and the co-pilot would enter the coordinates in the INS. The co-pilot would then repeat the coordinates and the Captain would ensure the read-back was correct.
Under this system you would think that there would not be a mix-up as the captain and co-pilot would both verify the information. The biggest chance of a mistake would be if the coordinate was written down wrong. Such as what happened on Varig Flight 254.

Captain Garcez consulted the flight plan for the magnetic heading to Belém; the flight plan read 0270. Garcez interpreted this as 270 degrees, but the intended meaning was 027.0 degrees.

I'm not a pilot, but it surprises me that neither pilots would know where they were going enough, at a situational awareness level, to know the difference between West and North-Northeast. But there you go! I suppose they fly around in so many directions on such a flight, and via so many intermediate points that you lose that kind of awareness.

Thanks, @DLH, for that info about Flight 254.  That is an error that makes some sense.

I did my flight training in Fairbanks, a bit north of Anchorage.  The compass deviation was about 17 degrees.  https://www.ngdc.noaa.gov/geomag-web/#declination  -  Then I would set it in the gyro compass before taking off.  I gather that "compass" in this context must have been simply in reference to the take-off point departure direction.  And I would presume that it would point towards the great-circle route to their destination.  I am amazed that the error was so slight at takeoff that it wasn't noticed, yet with catastrophic results.

The theory that I dimly recall was that when a route was manually programmed using waypoints created from Lat/Long data, the crew SOP was they were supposed to enter the waypoint data in each FMS separately and compare the two resulting routes so that random key input errors were likely to show up.  Instead, because they were in a rush, they entered the route in one FMS then copied it to the other and a keying error putting a waypoint 60nm west (or something like that) of where it was supposed to be went undetected.

Being in a rush is what caused Challenger to blow up, so I can understand that.

@SDsolar "Being in a rush is what caused Challenger to blow up" Not really... (at least not entirely)

Yeah Challenger was really a complex situation of confirmation bias, denial, bending to pressure, and wishful thinking all rolled into one, resulting in breakdown of an entire engineering/operational checks and balances process.

Point taken.  That was not the entire reason for Challenger.  In fact, it was really caused by the way they assessed risk factors, according to Feynman:  https://science.ksc.nasa.gov/shuttle/missions/51-l/docs/rogers-commission/Appendix-F.txt - but schedule pressure is what caused them to cut corners.  My comment was really just saying that this is an understandable reason why they might be in a hurry even at the cost of using an unsafe method of programming the flight-management system.  I wonder if they were just tired from too many hours on duty.

Yes.  I've made FMS entry errors that went undetected when my capt and I reviewed the waypoints... because we were in a big rush.  We were flying around in a big circle in a corporate jet (a pre-delivery test) and we left off a waypoint cutting off one of the corners of our polygon route.  Instead of busting us, ATC was kind enough to offer us a revised clearance when the controller saw us turning to the next-after waypoint instead of the next one.  My capt was doing the radios and he read back the revised clearance adding "and thank you very very much".


text:
How can someone get FAA commercial flight training as part of an aviation degree?
If someone can't afford to pay for flight training directly, is it possible to get commercial flight training with financial aid as part of a college degree?

For the UK answer, see: Do any UK universities include PPL/Commercial flight training as part of an aviation degree?

ERAU's cost calculator estimates $120,000 for tuition, books, room and board over 4 years and around 90,000 for flight training. That is 210,000 in student loans and the monthly payment wont be pretty, especially as the only aviation job open to you when you walk out the door is likely instructing until you have the experience for 135 or 121 operations.

In the US, there are 2 ways to become a certificated civilian pilot: Part 61 and Part 141.
Part 61 is done in informal classes and flights at a local flight school.
Part 141 is a professional pilot training program, with uniforms, classrooms, a full-time staff, and a uniform fleet of aircraft.
There are numerous US universities that offer bachelors' degrees using a part 141 program. You can find a list of such programs here.
Furthermore, many of these schools, such as Embry-Riddle, take the FAFSA, which is the  process for obtaining financial aid as for any other program.
After graduating from one of these programs, you will have obtained all the training necessary to work as a flight instructor, or as a commercial pilot under Part 119

Private Pilot Single Engine
Instrument Pilot Single and Multi-Engine
Commercial Pilot Single and Multi-Engine
Flight Instructor Single Engine
Flight Instructor Instrument
Multi-Engine Flight Instructor

You will have also earned either an Associates or Bachelors degree, usually in something like Aviation Engineering or Aviation Operations.
You will not, however, have flown enough hours to get a job flying air taxi or cargo under Part 135, which requires 500 hours to be the pilot-in-command.

A part 61 program can be quite professional, you dont need to be 141 to have the things you use to describe it. Part 141 is a structured, approved curriculum that allows certain things 61 does not and some subtle differences in requirements.

No you don't, but that's the way it is. And this is a question about university programs, which are all 141

Its also worth mentioning a university degree + flight training program will likely cost more than either a degree or flight training alone costs combined. If you cannot pay for training can you afford the massive student loan debt you'll incur in such a program?

Somebody must be going into these programs. I don't think it's the 1%ers

no, not only 1%ers.  It was also the first officers I flew with that told me of their struggles paying off their loans on first and second year FO pay and wishing they'd gone a different route.

I did a Part 61 program at Embry-Riddle for my PPL.  It was almost identical to their 141 program, but I'm not pursuing a career in commercial aviation (engineering major) so I wanted the freedom available with Part 61.

ATP offers to become an airline pilot for ~$75,000 (including housing). They are Part 141.

In general, the colleges which offer flight training do so at premium costs.  Frequently connected students will conduct their flight training with other providers, or during the summer, to reduce costs. There are quite a few community colleges also offering aviation programs, and their cost points are frequently more favorable than places like Embry-Riddle and Daniel Webster.  I have provided CFI initial training and signoffs to quite a few Daniel Webster students.